Not Applicable
Not Applicable
Not Applicable
(1) Field of the Invention
The invention relates to a device for conveying a medium from a container into a tank and for determining the quantity of the medium, having a conduit between the container and the tank, a conveying device connected to the conduit and a device for separating gas from the medium. The invention also relates to a method for conveying a medium from a container into a tank and for determining the quantity of the medium, in which the medium is transported via a conveying device and a conduit and gas absorbed by the medium is separated.
Such devices and methods are used in the most varied fields, such as e.g. in dairying or the distribution of fuels.
In the dairying sector a tank truck regularly visits certain milk producers and removes there the milk which has e.g. been produced during the course of a day from one or more storage containers. It is particularly important that the milk quantity removed is precisely measured and recorded, because it is on this basis that a subsequent settlement of account takes place between producer and customer. Therefore high demands are made on the quality of the quantity measurement, which is illustrated by the fact that legal regulations exist with regards to the calibrations and the quality of the measured results.
In order to meet these high demands it is necessary to minimize possible measurement errors. A particularly serious measurement error only eliminatable with a certain apparatus expenditure results from the fact that e.g. the milk is enriched with air during the removal process by pumps or the like and this leads to a more or less pronounced frothing of the milk. Thus, prior to the actual quantity measurement air separation must take place. Therefore in most prior art devices and methods the milk is firstly supplied to an air separator, where it remains until adequate degassing has occurred and is only then supplied via a flowmeter to the tank to be filled.
(2) Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In the Federal Republic of Germany there is e.g. a standard (DIN 19217: 1997-11), which contains strict regulations relating to air separation (cf. therein section 2.10.2). The technical features given in the DIN form the preambles of the independent claims. The DIN prescribes that in order to fulfil the calibration requirement the gas separator must be a separate component of the installation. This leads to problematic high apparatus costs. In addition, in the case of installations having a separate gas separator, as prescribed by the DIN, the aforementioned time lag problem occurs during the conveying of the medium, because it must in the meantime remain in the air separator. Thus, EP 626 567 B1 already proposes a flowmeter, which even in the case of air-freighted milk is able to sufficiently accurately determine the volume. However, this intrinsically satisfactorily operating device and the method performed by it are comparatively complicated and consequently require improvement.
DE 33 19 277 A1 discloses a float for a level control provided in an inner chamber of a milk container. The milk level is determined in that the float interior contains a magnet, which interacts with a permanent magnet inside a dipstick.
EP 806 636 A1 also discloses a device for determining the level, in this case in aircraft tanks. This device has the noteworthy feature that the level determination functions according to the so-called magnetostrictive principle, i.e. according to a method which utilizes the transit time of ultrasonic pulses produced by magnetic fields.
The object of the invention is to provide a volume determination device permitting a particularly accurate determination of the volume in the case of minimum apparatus cost and whilst avoiding measurement errors caused by gas occlusion. In addition, a method is provided for the filling of a tank and for determining the filling level, which implement the advantages of the device according to the invention.
This object is achieved with a device according to claim 1 and a method according to claim 18.
The device according to the invention is based on the prior art in that the device for separating gas and the tank form an integrated unit, that a filling level measuring device is substantially provided in the interior of the tank for determining the position of at least one boundary surface of the medium in the tank and that the filling level measuring device has at least one dipstick. This device renders unnecessary the use of a separate air separator, although this would not appear possible on the basis of the prior art, particularly in view of the aforementioned DIN 19217: 1997-11. Air separation initially takes place in the tank to be filled or the filled tank, which is possible in that the volume measurement determined by level measurement takes place in an extremely precise manner in the tank and not, as in the prior art, exclusively through a flowmeter upstream of the tank. This considerably reduces apparatus costs.
The device according to the invention is particularly advantageous if the filling level measuring device has a transsonar displacement transducer coupled to a computer operating according to the magnetostrictive principle and which is equipped with at least one dipstick and at least one float, the float or floats being equipped with at least one magnet. The magnetostrictive principle is based on the phenomenon that two intersecting magnetic fields cause a deformation of the metal in which they are focussed. If an exciting current pulse is supplied to the dipstick, this leads to an axially symmetrical exciting magnetic field with respect to said dipstick. This interacts with the intersecting magnetic fields of the float magnets, so that there is a brief deformation and a resulting ultrasonic pulse in the dipstick acting as a waveguide. Knowing the velocity of sound in the waveguide, conclusions can be drawn from the position of the magnets and consequently of the float from the transit time of the ultrasonic pulse through the dipstick up to a receiver preferably positioned terminally on the dipstick. Displacement transducers of this type are well known. As a result of the thus equipped device it is possible to measure the float position to an order of magnitude of 10 xc3xa6. In addition, transsonar displacement transducers are long term-stable and consequently fulfil the strict legal requirements concerning calibration and measuring accuracy.
It is advantageous for the dipstick to be fixed to the top of the tank. This permits an easy removal and fitting of the dipstick, which can e.g. be useful in connection with maintenance and cleaning.
It is particularly advantageous to provide a reference signal generator on the underside of the tank substantially on the dipstick axis and for the dipstick to penetrate the reference signal generator. The reference signal generator emits a filling level-independent signal, so that the receiver receives two generally successive signals. Through the measurement of the transmit times of both signals and subtraction it is possible to eliminate a measurement error as a result of the e.g. temperature-caused linear extension of the dipstick. Through the placing of the reference signal generator on the underside of the tank and the dipstick penetrating the same, the float can pass into the lower area of the tank and generate corresponding filling level signals. As a result of the free penetration of the reference signal generator, the dipstick is not prevented from any temperature-caused extension, so that this can occur without stressing the system.
It is also advantageous to fix the dipstick to the underside of the tank, particularly in view of possibly varying design possibilities.
The displacement transducer is preferably operated with a measuring frequency of 500 Hz. As a result of this high repetition frequency a quasi-continuance measurement is possible.
The float is advantageously a double float for density measurement. Thus, apart from the filling level measurement, further information concerning the state of the medium is received.
It is further advantageous if the dipstick is surrounded by a smoothing or calming pipe, which has individual openings for the passage of the medium. This in particular leads to advantages in conjunction with the use of the device according to the invention in tank trucks. Through the movement of the truck the liquid surface is normally subject to considerable movement and the calming of this surface movement can take up an undesirably long period of time. As a result of the dipstick being surrounded by a calming pipe, which is connected to the remaining tank volume by openings using the principle of communicating pipes, in the decisive area, namely that area directly surrounding the dipstick, a much faster calming occurs and consequently there are inconsiderable time and cost economies.
It is also possible to use a computer, which has a software-based digital filter and which is suitable for converting the filling level values into volume values. It is possible to use a digital filter due to the high measuring frequency which is preferably present. In principle, it is possible to use all known filters, such as e.g. Bufterworth, Tschebyscheff or Bessel filters and the like. The computer has access to data describing the tank geometry, so that said conversion can take place. The advantage is that directly the interesting volume data and not the primarily measured filling level data can be displayed.
The filling level measuring device can also have a capacitive or potentiometric dipstick. An ultrasonic measuring device can also be used. This increases the flexibility concerning the possibilities of use, e.g. in conjunction with the different physical characteristics of the media in question.
Particularly in the case of symmetrical tanks, the dipstick is preferably arranged in the volumetric centre. This minimizes measuring errors as a result of an inclination of the tank.
It is also possible to provide devices for measuring the temperature of random components, preferably within the tank, the results of the temperature measurements being inputtable into the computer. Thus, there can be a correction of temperature-caused measuring errors on the software plane.
It is particularly advantageous if the computer is connected to a biaxial inclinometer. As a result data concerning the angular position of the tank can be inputted into the computer, which represents a further correction possibility for increasing measuring accuracy.
The system is preferably equipped with a sampler, which removes the sample quantities proportional to the conveyed volume. Such a proportional removal is advantageous, because it leads to a representative sample having the same qualitative composition as the total conveyed quantity. Proportional removal is possible, because a quasi-continuous volume measurement can be performed by the device according to the invention and therefore direct information on the volume flow is available.
In this connection or also for further increasing the measuring accuracy, the volume measurement can be additionally assisted by a possibly provided flowmeter. The use of such a flowmeter is particularly useful if already degassed milk is to be transferred from a smaller into a larger tank. It is pointed out in this connection that through the use of a small tank the absolute measuring accuracy is additionally increased. In particular, the measuring error is reduced in that the cross-sectional surface of the tank is decreased in favour of its height.
The conduit preferably has a valve means, which comprises a check or non-return valve and a valve controllable by the computer. The check valve and the controllable valve can also be implemented in the form of a single valve. The check valve prevents the flow back of medium from the tank into the container and forms the volume calibration zero, whereas the computer-controllable valve is e.g. closed if tank overfilling threatens. In order to continue takeover it is e.g. possible in this case to open a valve to a further tank or a farther chamber.
It can also be advantageous for the conduit to have coils. The coils can assist the degassing of the medium, because as a result of centrifugal force the medium is forced to the outer wall of the conduit, whilst the gas can pass out in the inner area. If the gas is provided with a possibility to leave the conduit system, as a result of this measure already partly degassed medium enters the tank.
The conveying device is preferably a self-priming impeller pump.
Advantageously the system is operated by vacuum.
It can also be advantageous for the computer to be connected with the adjustable or controllable valve or valves and/or with the conveying device. This makes it possible to control or regulate the delivery, as a function of random data supplied to the computer.
Preferably a computer is provided permitting the recording of random measured results and with which random process parameters can be controlled, monitored and regulated.
The method according to the invention is based on the prior art in that the gas separation at least partly takes place in the tank and that the filling level in the tank is measured by a filling level measuring device. The method makes it possible to obviate the use of a separate air separator, because the filling level and consequently the volume in the tank are measured, which avoids any need for an air separation prior to the passage of the medium through a flowmeter.
Preferably the filling level measuring method is based on the magnetostrictive principle, which permits a particularly accurate filling level measurement.
It is particularly advantageous if the filling level is determined by establishing the difference between the transit times of a signal generated at the location of a float and a signal generated at a fixed location with respect to the tank. As a result of such a subtraction the method is made independent of a possible e.g. temperature-caused extension of the dipstick.
Preferably a measurement of the temperature at random points within the system, particularly in the actual medium, the angular position of the tank and/or the density of the medium takes place, the measured results being supplied to a computer. As a result of these measurements the measured results can be advantageously corrected with respect to the volume. Particularly with regards to product detection or quality testing, density measurement plays an important part.
Preferably a computer is able, while incorporating random inputs, to open or close the valve to the tank, control and also monitor the conveying capacity of the conveying device.
A digital filter is preferably used in the computer for correcting surface fluctuations. This is in particular possible through the preferred use of a measuring frequency of 500 Hz, so that there is a quasi-continuous measurement. This permits the use of virtually random digital filters and the time necessary to obtain a reliable measured result is reduced by several orders of magnitude.
It is advantageous if part of the gas is separated before the medium enters the tank, because this further increases the filling rate and the reliability of the measurement.
It is also preferable during the filling of the tank to continuously measure the speed of rise of the float. With a correct operation of the installation this must be correlated with an expected pump efficiency, so that if correlation does not exist it can be concluded that there is a fault in the installation.
Preferably during the filling process a representative sample is taken, said sample quantity being correlated with the volume increase. The latter ensures the necessary product quality.
Advantageously use is made of a computer for recording random measured results and for controlling, monitoring and regulating random process parameters. This preferred integration permits a variable and central control of the system.